The 'Fat-Burning Zone': A Fitness Myth Debunked

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I teach Indoor Cycling classes and always use my CS 300 Polar heart rate monitor. I also maintain a training log online and an Excel spreadsheet, which separates fat/carb calories. I have 7 months of data and it confirms the information written in this article.
In an intense 45 minute Spinning session I can burn as much as 650 - 700 calories, 35% - 40% being fat cals, at 80% - 85% of HR max. However, working at 75% of max I find that I can burn around 550 calories, with up to 60% of those being fat cals. Therefore, I'm burning more fat cals working at a lower intensity. I'm trying to find a happy medium.
My question: Is it more efficient to burn more fat cals or more total cals when working within a specific time frame (45 minutes)?

http://thebuddhistcyclist.blogspot.com/ of TN 12:20AM March 13, 2009

Have any studies been done that compares and measures fat burning at a low intensity(55%-65% of Max) verses a high intensity (75%-85%)? If so, how can I get access to the data?

christine ragusa of NY 4:19PM March 12, 2009

Thanks for clarifying the fat buring zone mystery. I often tell my clients who want to lose weight, to target their heart rate for their cardio workout so that their body gets exhausted. My rule of thumb goal is 85% of max heart rate because most people are exhausted when they reach and maintain this heart rate goal for 5-10 minutes. What I always understood was that you exercise at a target heart rate that will force your body to use up its carb energy source, and then have to go to fac cells for energy. The physical signs are breathing hard, perspiring and talking words (not necessarily sentences). BAsed on this article I'm wondering if this assessment is still valid.

Benita Perkins of NJ 2:43PM March 03, 2009